Nociceptin/orphanin FQ increases ANP secretion in neonatal cardiac myocytes

Nociceptin (N/OFQ) is a novel heptadecapeptide with an amino acid sequence similar to that of endogenous opioid peptide dynorphin A. Dynorphin have been reported to increase the secretion of atrial natriuretic peptide (ANP) via selective activation of kappa-opioid receptor in cultured atrial cardiocytes. The present study was designed to investigate the direct effect of N/OFQ on the ANP secretion in cultured neonatal rat cardiac myocytes via N/OFQ receptor (NOP) activation. The secretion of ANP from cultured neonatal cardiac myocytes was increased in terms of incubation time. N/OFQ, at a dose of 0.3, 1, 3, and 10 microM, caused increases in ANP secretion in a dose-dependent manner. The N/OFQ-induced ANP secretion was completely antagonized by antagonists of NOP, 1 microM each of [Phe1 (CH2-NH) Gly2] nociceptin (1-13)-NH2 ([FG]N/OFQ(1-13)NH2) or naloxone benzoylhydrazone. In contrast, naloxone (1 microM), the non-selective opioid receptor antagonist, did not alter ANP response to N/OFQ. N/OFQ at 3 microM inhibited basal and forskolin-stimulated cAMP production, which was partially antagonized with the pretreatment of [FG]N/OFQ(1-13)NH2. An increase in ANP secretion by N/OFQ was also partially blocked by the pretreatment of forskolin. Homologous competition studies in neonatal cardiomyocyte membranes revealed the presence of two distinct sites. The high affinity site (10.9 +/- 1.6 nM) was far less abundant than the low affinity site. Therefore, these results suggest that N/OFQ causes an increase in ANP secretion in cultured neonatal cardiac myocytes by decreasing cAMP through its binding sites.

4-Hydroxy-6-oxo-6,7-dihydro-thieno[2,3-b] pyrimidine derivatives: synthesis and their biological evaluation for the glycine site acting on the N-methyl-D-aspartate (NMDA) receptor

Bioisostere approach has been shown to be useful to augment potency or to modify certain physiological properties of a lead compound. Based upon well documented bioisosterism, an isosteric replacement of benzene ring of 4-hydroxy-2-quinolone compound (L-695902) with a thiophene moiety was carried out to prepare the title compounds, 4-hydroxy-6-oxo-6,7-dihydro-thieno[2,3-b] pyrimidines 15. The resulting bioisosteric compounds 15 were evaluated for their antagonistic activity (binding assay) for NMDA receptor glycine site.

Characterization of antidepressant-like effects of p-synephrine stereoisomers

We previously reported that p-synephrine has antidepressant-like activity in the murine models of forced swimming and tail suspension. In the present study, we characterized antidepressant-like effects of p-synephrine stereoisomers in both in vivo and in vitro systems. In the tail suspension test, S-(+)-p-synephrine (3 mg/kg, p.o.) reduced the duration of immobility, while R-(-)-p-synephrine (0.3-3 mg/kg, p.o.) had no effect. S-(+)-p-synephrine (0.3, 1 and 3 mg/kg, p.o.) and R-(-)-p-synephrine (1 mg/ kg and 3 mg/kg, p.o.) significantly reversed the reserpine (2.5 mg/kg, i.p.)-induced hypothermia. S-(+)-p-synephrine was more effective than R-(-)-p-synephrine in inhibition of both [3H]noradrenaline uptake in rat cerebral cortical slices (maximal inhibition 85.7 +/- 7.8% vs. 59.8 +/- 4.3%; EC50 5.8 +/- 0.7 microM vs. 13.5 +/- 1.2 microM) and [3H]nisoxetine binding (Ki 4.5 +/- 0.5 microM vs. 8.2 +/- 0.7 microM). In contrast, R-(-)-p-synephrine was more effective than S-(+)-p-synephrine in stimulation of [3H]noradrenaline release from rat cerebral cortical slices (maximal stimulation 23.9 +/- 1.8% vs. 20.1 +/- 1.7%; EC50 8.2 +/- 0.6 microM vs. EC50 12.3 +/- 0.9 microM). The stimulatory effect of R-(-)-p-synephrine on [3H]noradrenaline release was inhibited by nisoxetine (100 nM), but tetrodotoxin (1 microM) and elimination of extracellular calcium had no effect. It is suggested that S-(+)-p-synephrine has more effective antidepressant-like activity than R-(-)-p-synephrine.

Receptor selectivity of Met-enkephalin-Arg6-Phe7, an endogenous opioid peptide, in cerebral cortex of human and rat

This study was undertaken to examine the receptor selectivity of Met-enkephalin-Arg6-Phe7 (MERF) employing radioreceptor binding assays in human cerebral cortex membranes, and to elucidate the responsible receptors that mediate the regulatory action of MERF on high (20 mM) K+-stimulated release of [3H]norepinephrine ([3H]-NE) in rat cortex slices. Specific binding of [3H]MERF was inhibited by DAMGO, Tyr-D-Arg-Phe-Sar(TAPS), bremazocine and ethylketocyclazocine (EKC), but not by U69,593 (U69) and DPDPE. MERF showed high affinity for specific binding sites of [3H]DAMGO. However, MERF had little influence on the specific binding of [3H]DPDPE, [3H]U69 and [3H]diprenorphine ([3H]DIP) in the presence of 1 microM each of DAMGO, DPDPE and U69. In [3H]NE release experiments using rat cortex slices, DAMGO, MERF and EKC, in order of their potency, inhibited K+-stimulated release of [3H]NE. The inhibitory effects of MERF and DAMGO were more sensitive than that of EKC to antagonism by CTAP, nor-binaltorphimine (nor-BNI) and naloxone. These results suggested that MERF possesses high affinity for mu-receptors, but not for delta-, kappa1-, and very low affinity for kappa2-receptors in human cerebral cortex membranes. Also, the inhibitory effect of MERF on the K+-stimulated release of [3H]NE appears to be mediated by mu-receptors in rat cerebral cortex slices.